The goal of the proposed research remains the elucidation of the neurobiological mechanisms underlying the abuse-promoting and psychotomimet c effects of phencylclidine (PCP) and related drugs. During the previous project periods, we identified specific PCP receptors in brain membranes. The properties of these sites are consistent with their mediating the uniqu actions of PCP-type drugs. Work in this and other laboratories has shown that PCP-like drugs are noncompetitive antagonists of NMDA class of excitatory amino acid receptors of brain. In the proposed research, we sha l determine the biochemical and neuroanatomical bases of the PCP-NMDA recepto interaction. The effects of NMDA receptor ligands and modulators upon specific binding of PCP-receptor ligands will be determined at equilibrium and kinetically. The specific mechanisms by which NMDA agonists and modulators alter binding of PCP receptor radioligands will be elucidated. We have identified multiple components of radioligand binding to PCP receptors. The hypothesis will be tested that these correspond to closed a d open states of the NMDA channel complex. The number of molecules of NMDA agonist and of blycine required for maximal stimulation of radioligand binding to PCP receptors will be determined. Quantitative autoradiographic determinations of PCP and NMDA receptor distributions using selective radioligands will be compared in adjacent brain sections in order to establish the extent of their co-localization. Quantitative PCP receptor autoradiography will be carried out in the presence and absence of direct NMDA receptor agonists, antagonists and modulators in order to determine whether the high-affinity forebrain type of PCP receptor, but not the low- affinity hindbrain type of receptor, may be associated with NMDA channels, and whether the functional relationship of PCP with NMDA receptors is the same throughout the brain. During the previous project period we successful y solubilized and reconstituted into proteoliposomes active PCP receptors whi h are regulated by NMDA agonists and antagonists. We shall determine the biochemistry of the PCP-NMDA receptor interaction in this preparation and ultimately will introduce the proteoliposomes into synthetic lipid bilayers which will permit the first direct comparison of electrophysiological with receptor binding studies of the PCP-NMDA receptor interation. The results of these experiments will reveal the role of NMDA receptors in mediating th abuse-promoting and psychotomimetic properties of PCP-like drugs and may le d to the possibility of development of new therapeutic interventions targetin specific drug-abuse and mental-health disorders which may be related to dysfunction of the NMDA-PCP system. We have collected a number of specimen of well-preserved postmortem human brain tissue; these will be utilized to determine the PCP-NMDA receptor interaction in detail for critical comparis n with the findings in the rat brain, and to establish a baseline for future studies in brain tissue derived from individuals who had suffered from drug abuse or mental health disorders.